Since titanium alloy is good in terms of the specific strength, it has been used in the fields of aviation, military, deep-sea survey, and the like. In the filed of automobile as well, titanium alloys have been used in valve retainers, connecting rods and so forth of racing engines. Further, since titanium alloy is good in terms of the anti-corrosiveness as well, it has been often used under corrosive environments. For example, it has been used as materials for chemical plants, oceanic architectures, and so on, and, furthermore, in order to inhibit the corrosion by anti-freezing agents, it has been used for lower front bumpers, lower rear bumpers, and the like. Moreover, aiming at its light-weightness (specific strength) and anti-allergenicity (anti-corrosiveness), titanium alloy has been used for accessories such as wristwatches. Thus, titanium alloys have been used in various and diversified fileds, as for representative titanium alloys, there are, for example, Ti5-Al-2.5Sn (α alloy), Ti-6Al-4V (α-β alloy), Ti-13V-11Cr-3Al (β alloy), and so forth.
By the way, the good specific strength and anti-corrosiveness have been attracting attention, however, its good elasticity has been about to attract attention recently. For example, titanium alloys which are good in terms of the elasticity are about to be used for products adaptable to living bodies (for instance, artificial bones, and the like), accessories (for example, frames of eyeglasses, and so forth), sporting goods (for instance, golf clubs, and so on), springs, and the like. Specifically, when titanium alloy of high elasticity is used for artificial bone, the artificial bone has elasticity close to that of human bone so that it is good in terms of the adaptability to living bodies in addition to the specific strength and anti-corrosiveness.
Further, an eyeglasses frame, comprising highly elastic titanium alloy, fits flexibly to heads, gives no oppressive feelings to wearers, and is good in terms of the shock-absorbing property.
Furthermore, when highly elastic titanium alloy is used for shafts or heads of golf clubs, it is said that flexible shafts or heads of low eigenfrequency can be obtained and that the driving distance of golf ball can be extended.
Moreover, when highly elastic titanium alloy is used for springs, light-weight and large elastic limit springs can be obtained.
Under such circumstances, the present inventors thought of developing a titanium alloy by which the utilization expansion can be further intended in a variety of fields and which is of high elasticity (high elastic deformation capability) and high strength (high tensile elastic limit strength) transcending the conventional levels. Then, the conventional technologies regarding titanium alloys which are good in terms of the elasticity were first surveyed, and consequently the following publications were discovered.